Hyaluronan can be non-enzymatically linked to protein through an alkali sensitive bond

Evaluating specific adhesion of Plasmodium falciparum-infected erythrocytes to immobilised hyaluronic acid with comparison to binding of mammalian cells

A feature of infection with Plasmodium falciparum is the ability of parasite-infected erythrocytes to adhere to vascular endothelial cells and accumulate in vital organs, associated with severe clinical disease. Hyaluronic acid was recently identified as a receptor for adhesion and has been implicated in mediating the accumulation of parasites in the placenta. Here, we report in vitro assays to measure specific adhesion of infected erythrocytes to hyaluronic acid that is distinct from binding to chondroitin sulphate A, another glycosaminoglycan implicated as a receptor in placental malaria. In this study, specific adhesion of mature stage infected erythrocytes to hyaluronic acid of high purity immobilised on plastic surfaces was abolished by pre-treating hyaluronic acid with a specific hyaluronate lyase from Streptomyces, whereas the same treatment of chondroitin sulphate A had little effect. Adhesion to hyaluronic acid could not be explained by the presence of chondroitin sulphate A or other glycosaminoglycans in the hyaluronic acid preparations. Chinese hamster ovary cells bound in a similar manner in the assays and confirmed that hyaluronic acid was appropriately immobilised for cell adhesion. In contrast to parasites, these cells did not adhere to chondroitin sulphate A. The adsorption of hyaluronic acid onto plastic surfaces was also confirmed by the use of a specific hyaluronic acid-binding protein. Fixing cells with glutaraldehyde at the completion of adhesion assays reduced the number of parasites remaining adherent to hyaluronic acid, but not to chondroitin sulphate A or CD36. These findings have important implications for understanding and evaluating interactions between P. falciparum and hyaluronic acid that may be involved in disease pathogenesis.

Extracellular matrix hyaluronan is a determinant of the endothelial barrier

We measured the hydraulic conductivity (Lp) of the extracellular matrix (ECM) obtained after detaching bovine pulmonary microvascular endothelial (BPMVEC) and bovine pulmonary arterial endothelial cell (BPAEC) monolayers from the ECM at different days postseeding. From day 1 to day 5 in culture, the total Lp (i.e., of cell monolayer + ECM) decreased from basal values of 17.1 +/- 4.0 to 8.5 +/- 1.6 x 10(-6) cm.s-1.cmH2O-1 in BPAEC (P < 0.05) and 7.6 +/- 1.1 to 3.7 +/- 0.8 in BPMVEC (P < 0.05), respectively, and on day 5 the total Lp values were lower in BPMVEC than in BPAEC (P < 0.05). On the 5th day, ECM Lp was 55.0 +/- 8.3 in BPAEC and 10.7 +/- 0.9 cm.s-1.cmH2O-1 in BPMVEC (P < 0.05), indicating that the contribution of ECM to the total Lp was greater in BPMVEC than in BPAEC. Treatment of [3H]acetate-labeled ECM with Streptomyces hyaluronidase (HAse; 6 U/ml for 10 min) released sixfold greater radioactivity in BPMVEC compared with untreated BPMVEC controls; a similar treatment of BPAEC did not release detectable radioactivity indicative of a higher hyaluronan content in the BPMVEC ECM. HAse treatment reduced the differences in total Lp between BPMVEC and BPAEC at different days postseeding. Moreover, on the 5th day after seeding, the ECM Lp of BPMVEC increased to a greater extent after HAse treatment than the ECM of BPAEC. These data indicate that the hyaluronan component of the ECM is an important determinant of the endothelial liquid-exchange barrier.

Synovial hyaluronate in rheumatoid arthritis binds C1q and is covalently bound to antibodies: a model for chronicity

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Binding and degradation of hyaluronan by human breast cancer cell lines expressing different forms of CD44: correlation with invasive potential

In the present study, we examined a panel of human breast cancer cell lines with regard to their expression of CD44 and ability to bind and degrade hyaluronan. The cell lines expressed varying amounts of different molecular weight forms of CD44 (85-200 kDa) and, in general, those that expressed the greatest amounts of CD44 were the most invasive as judged by in vitro assays. In addition, the ability to bind and degrade hyaluronan was restricted to the cell lines expressing high levels of CD44, and both these functions were blocked by an antibody to CD44 (Hermes-1). Moreover, the rate of [3H]hyaluronan degradation was highly correlated with the amount of CD44 (r = 0.951, P < 0.0001), as well as with the invasive potential of the cells. Scatchard analysis of the [3H]hyaluronan binding of these cells revealed the existence of significant differences in both their binding capacity and their dissociation constant. To determine the source of this deviation, the different molecular weight forms of CD44 were partially separated by gel filtration chromatography. In all cell lines, the 85 kDa form was able to bind hyaluronan, although with different affinities. In contrast, not all of the high molecular weight forms of CD44 had this ability. These results illustrate the diversity of CD44 molecules in invasive tumor cells, and suggest that one of their major functions is to degrade hyaluronan.

Age-dependent changes of hyaluronan in human skin

Hyaluronan is a major component of the extracellular matrix of skin. The large volume of water of hydration associated with hyaluronan may be a mechanism for maintaining the normal hydration of skin. As such, decreasing levels of hyaluronan deposition might underlie the changes associated with the aging process. To test this hypothesis, hyaluronan levels were determined in extracts of skin obtained at autopsy from individuals of different ages. However, no significant differences in hyaluronan concentrations were found. The distribution of hyaluronan polymer sizes in various extracts did not change as a function of age as measured by size exclusion chromatography. However, major differences in hyaluronan extractability did occur as a function of age. Sequential extraction was performed utilizing 1) 0.1% Triton X-100, 2) 4 M guanidine-HCl, and 3) papain digestion, to release species of hyaluronan progressively more tightly associated with tissue. With advancing age, hyaluronan polymers became progressively more tissue associated. The proportion of hyaluronan released after papain digestion increased from 7% of the total in fetal to 23% of the total in senescent skin. Finally, histolocalization of hyaluronan was examined in full-thickness sections of human skin of different ages. Major differences in compartmentalization were found. We conclude that neither the concentration nor polymer size of hyaluronan changes as a function of age. However, enhanced association with tissue occurs, presumably through hyaluronan-binding proteins and alterations in the histolocalization of hyaluronan. Such observations may underlie some of the changes in human skin that occur with aging.